1. Field of the Invention
The present invention relates to a dual mass damping flywheel for coupling an internal combustion engine in rotation to a transmission system, in particular for a motor vehicle.
2. Description of Related Art
Such a dual mass double flywheel is described in the document FR-A-2 749 904 wherein, a torque limiter is interposed operatively between a plate, constituting the reaction plate of a friction clutch, and an internal hub which is surrounded by the reaction plate.
The reaction plate and the hub are part of a secondary flywheel which is adapted, through a friction face of the reaction plate, to be coupled disengageably with a driven member of a transmission system, such as the input shaft of a gearbox of a motor vehicle.
The dual mass flywheel also comprises a primary flywheel which is arranged to be coupled in rotation to a driving shaft, such as the crankshaft of an internal combustion engine of a motor vehicle.
The secondary flywheel is mounted for rotation, by means of its hub, on the primary flywheel, which includes a generally transversely orientated element such as a plate which is parallel to the reaction plate of the secondary flywheel.
Resilient members are interposed operatively between the transverse element of the primary flywheel and the hub of the secondary flywheel so as to couple the secondary flywheel elastically to the primary flywheel.
The resilient members may consist of curved springs, in particular pre-curved springs, which act circumferentially between abutment elements fixed with respect to the primary flywheel and arms which are provided at the outer periphery of a disc which is fixed with respect to the hub of the secondary flywheel. The arms are disposed between two abutment elements of the primary flywheel, in facing relationship with each other.
In another version, the resilient members act radially in the rest position of the dual mass damping flywheel.
In the document FR-A-2 749 904, the torque limiter has a friction ring which is provided with outwardly aligned lugs which extend through apertures formed in a ring with axial elasticity, which is fixed with respect to the hub.
The friction ring defines the flank of a groove, the other flank of which, and the base of which, are part of the outer periphery of the hub. The reaction plate has at its inner periphery an internal ring portion which is centered by the base of the groove and which is pinched between the flanks of the groove. This arrangement gives satisfaction because it is of reduced axial size.
The need exists for an arrangement that makes it possible to take advantage of the hub without increasing axial size.
An object of the present invention is to respond to the aforementioned drawbacks in the prior art.
According to the invention, a dual mass damping flywheel of the type described above is characterised in that the internal hub is so configured as to delimit a cavity radially inwards of the internal ring portion of the reaction plate, in that, mounted inside the cavity, there is at least one abutment element which is fixed with respect to the friction ring and offset axially towards the primary flywheel with respect to the friction ring, and in that, radially inwards of the internal ring portion of the reaction plate, the axially acting resilient means bear on the abutment element and on at least one backing element which is fixed to a support member fixed to the internal hub, whereby to grip the ring portion between the flanks of the groove.
As a result of the invention the function of the torque limiter is improved, especially in terms of its torque transmitting capacity and its useful life, because it is possible to control precisely the load exerted by the axially acting resilient means because the latter act between an abutment element and a backing element, both of which may be of divided form, and which are part of two separate components. The support piece fixed to the hub is located radially inward of the friction ring and therefore has a small radial dimension.
Because of the cavity which is bounded by the internal hub, the same axial size is generally retained in the region of the torque limiter. In practice the axial size is reduced because there is no component superimposed on the friction ring, since the resilient means act radially inwardly of the internal ring portion. In addition, there are no longer any straightened up lugs. In general terms, the abutment element or elements are lodged within a cavity which is preferably open axially away from the primary flywheel. The solution is therefore simple and inexpensive, because the support piece fixed with respect to the hub is joined to the latter by means of rivets, which in one embodiment constitute articulating pivot pins for the resilient members, or fastening rivets for a disc which acts on the resilient members. The friction ring is preferably inclined in the rest position and is then straightened up, its inclination becoming smaller, after it has been fitted, under the action of the resilient means so that the friction ring closely matches the form of the ring portion of the reaction plate, and the performance of the torque limiter is improved. The torque limiter is then able to transmit a greater amount of torque.
It will also be appreciated that the axially acting resilient means are located radially inwards of the reaction plate of the secondary flywheel. As a result, the resilient means are cooler than in the prior art, because they are further away from the friction face of the reaction plate.
This arrangement favours a reduction in axial size, so as better to control the characteristics of the torque limiter and improve the useful life of the latter. The cavity in accordance with the invention favours cooling of the internal hub and therefore the bearing means which are interposed operatively between the hub and a central first hub of the primary flywheel.
The abutment element and the backing element are preferably orientated transversely, and are offset axially with respect to each other.
The axially acting resilient means may consist of a plurality of helical springs. Preferably, in order to reduce axial size the axially acting resilient means comprise a Belleville ring. They may for example consist of a diaphragm, that is to say a component which includes at its outer periphery a Belleville ring which is extended radially inwards by a central portion divided into lugs by slots which separate the lugs from each other.
The resilient means preferably consist of a Belleville ring. The Belleville ring or the diaphragm is in contact at its outer periphery with the abutment means and at its inner periphery with the backing element.
Because of the Belleville ring of the axially acting resilient means it is possible to increase the useful life of the torque limiter because the latter is less sensitive to wear than that in the prior art.
In this connection, this results from the fact that the Belleville ring works between two separate components so that it is possible to obtain better control of its characteristic curve (of force exerted as a function of deflection).
As is known, this characteristic curve has a form which is generally a portion of a sine curve, so that the initial force exerted by the Belleville ring is chosen beyond the maximum of the curve, that is to say for a deflection greater than that which corresponds to the maximum. This initial load is of course chosen to be close to the maximum of the characteristic curve.
In one embodiment, the base of the groove is defined by the hub which is hollow radially inwards of the internal ring portion, so as to form a cavity which is open axially away from the primary flywheel. The abutment element according to the invention is lodged within this cavity. The internal hub therefore has a reduced thickness radially inwards of the internal ring portion. More precisely, the base of the groove of the hub is provided by a sleeve portion the internal periphery of which serves to center the friction ring, with its outer periphery serving to center the internal ring portion.
This friction ring is coupled in rotation to the hub in mating cooperation.
For example, the abutment element is extended at its inner periphery by at least one transversely orientated lug which is engaged in a notch formed in the hub.
Preferably, at least two lugs and two notches are provided, these being in diametrically opposed positions.
Thus, with an open cavity formed in the hub, and one component additional to the torque limiter of the prior art, improved control of the function and characteristics of the torque limiter is obtained, and this is achieved generally within the same size limitations, and in practice within an axial size which is slightly reduced. As a result, for a given size, at least one of the flanks of the groove and at least one of the associated faces of the ring portion may be frusto-conical so as to increase the torque transmitted. By making the holes in the base of the cavity, that is to say in the hub, cooling of the torque limiter is improved. In another version, the hub has a reduced thickness radially inwards of the internal ring portion by virtue of a radial plate which it has for this purpose. It is the outer periphery of this radial plate that serves to center the reaction plate.
In one embodiment, the outer periphery of the radial plate is in intimate contact with an annular, axially orientated surface which joins the outer periphery of the internal ring portion to the side face of the reaction plate that faces towards the primary flywheel.
Debris will be produced by frictional contact of the radial plate with the ring portion. In order to evacuate this debris, notches are formed at the periphery of the radial plate.
In another version, the friction ring is coupled in rotation with the backing element by mating cooperation, through its abutment element. The abutment element comprises for example at least one lug which is engaged in an associated hole formed in the backing element.
In a further version, the backing element is provided with a press-formed element which is for example U-shaped and in which the lug of the abutment element is engaged. This solution is inexpensive because the hub remains unchanged.
Similarly, the solution in which the reaction plate is centered by a radial plate of the hub is advantageous because it enables radial size to be reduced due to the fact that the hub no longer has a central sleeve portion. It emerges from the foregoing that the backing element may serve to center the friction ring. For this purpose it is sufficient to give the abutment element of the friction ring at least two of the above mentioned lugs engaged in two holes, or two associated pressed out portions formed in the backing element.
The web portion may be distinct from the hub, being then fixed to the latter, for example by being applied by in situ moulding or seaming.
The same is true for the internal ring portion which can then be applied by in situ moulding or seaming on the reaction plate. This enables the thickness of the internal ring portion to be reduced and therefore enables axial size to be reduced. In general terms, the web portion or the internal ring portion may be assembled with the hub and the reaction plate, respectively, in any way.
The internal ring is for example of metal. The same is true of the web. These latter can be coated with a wear resistant layer, which is for example nickel or molybdenum based. These components can be made inexpensively in sheet steel hardened by a heat treatment operation. All of this enables the useful life of the dual mass flywheel to be increased because the internal ring portion becomes worn to a lesser extent than the internal ring portion formed integrally by moulding with the reaction plate, which is for example a casting.